In the early days of the original Mercy Hospital in Hempstead, five of the nuns who staffed the institution had to sleep on an open porch protected only by a canvas drop. Sometimes the snow came in on them.

This year, as Mercy Medical Center in Rockville Centre celebrates its 100th anniversary, it is a far different institution, with state-of-the-art equipment, 100,000 patient visits a year...

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In the early days of the original Mercy Hospital in Hempstead, five of the nuns who staffed the institution had to sleep on an open porch protected only by a canvas drop. Sometimes the snow came in on them.

This year, as Mercy Medical Center in Rockville Centre celebrates its 100th anniversary, it is a far different institution, with state-of-the-art equipment, 100,000 patient visits a year and few nuns -- only three remain on the staff.

The anniversary of the oldest hospital run by the Roman Catholic Church in Nassau County "is a momentous event," said Dr. Aaron E. Glatt, the hospital's chief administrative officer.

Mercy is kicking off a yearlong series of events to mark the anniversary, including a Mass presided over by Bishop William Murphy on March 10 at St. Agnes Cathedral in Rockville Centre.

The hospital will also host other activities, such as providing special gourmet dinners to the extended families of the 100th, 500th, 1,000th and -- if they get there -- 1,500th baby born at the hospital this year, said Ron Steimel, Mercy's chief operating officer.

In 1913, its first year, when it was operating out of a former 13-bed sanitarium in Hempstead, the hospital served 223 patients, said Sister Dolores Wisniewski, head of the Congregation of the Infant Jesus, the order of religious sisters that founded the Mercy Hospital.

It could handle 16 patients and 13 newborns at a time. Patients who could not walk to the small operating room on the third floor were taken up in an old elevator that was moved with ropes and pulleys.

The hospital can trace its origins to 1905, when three sisters from the France-based Congregation of the Infant Jesus arrived in Brooklyn from France. The sisters planned to go out West to work, but the bishop of Brooklyn, who then oversaw all of Long Island, persuaded them to stay in the area.

"From a professional point of view, it left much to be desired, but the homey atmosphere and the contagious spirit of love more than compensated for the lack of material resources," the congregation said in a book it published about its history.

Some of the sisters got sick or died of tuberculosis. The head of the order at the time thought fresh air and isolation could help stem the spread of the disease and had tents erected on the grounds for the sick sisters.

In the late 1920s, the congregation contemplated closing the humble hospital, but the bishop headed that off. By 1929, they managed to add a small new wing so the sisters did not have to sleep on the porch anymore.

In 1941, the hospital moved from Hempstead to its present location near Peninsula Boulevard and Southern State Parkway in Rockville Centre. It has steadily expanded, adding a maternity building in 1945, a convent in 1946 and an extension of the main hospital building in 1954.

Despite fiscal challenges in the last decade, the hospital is now operating in the black and has top-notch services in several areas, including the only Level III Neonatal Intensive Care Unit on the South Shore in Nassau, Glatt said. It has 375 beds, 700 attending physicians and 1,700 employees. The emergency room typically logs 40,000 patient visits a year.

Wisniewski said the hospital has been able to survive partly because of donations from the public and the church. "We didn't do it totally alone," she said. "We are indebted to them for helping us carry out our mission."